Such multi-layer components can be used as capacitors, varistors, or temperature-dependent resistors (thermistors) according to the configuration of the ceramic layers and the electrode surfaces. The body of varistors is often produced from a mixture of different metal oxides, for example, based on zinc oxide. Varistors have a non-linear voltage-dependent change in resistance, which is used for protecting electrical circuits from overvoltages. The resistance value of varistors falls as the applied voltage increases.
From the publication DE 199 31 056 A1, a multi-layer varistor is known, in which non-overlapping internal electrodes are arranged in the interior of the body for reducing the resistance. The internal electrodes are here contacted on the two end faces of the component by large surface-area contact layers, which allow SMD mounting of the component. A disadvantage of this conventional component is that due to the large surface-area contact layers, parasitic capacitances and inductances are built up, which make the precise setting of the electrical characteristics of the component difficult. Furthermore, such a component requires, accordingly, an inordinate amount of space for mounting, for example, on circuit boards, due to the large contact layers. Furthermore, above all, modules in this construction, in which several of these components are integrated, are also especially large and thus feature an especially low integration density.
From the publication DE 100 19 840 A1, a ceramic multi-layer capacitor with a first electrode structure is known, which has freely ending via contacts (blind ends). The shortest distance between the two electrode structures of the capacitor is determined by the distance of overlapping electrode layers.
From the publication WO2004/086432, a multi-layer varistor is known, in which for reducing the parasitic capacitances, the internal electrodes are connected by means of via contacts both to each other and to solder bumps on the bottom side of the body.
The use of such varistors as, e.g., ESD protection components in high-frequency data lines, however, presents problems. Parasitic capacitances in known multi-layer varistors still reach regular values of more than 60 pF, which makes them unsuitable for this application. Capacitances of this order of magnitude lead to the result that all of the signals are diverted to ground from a certain limit frequency and thus the data signal carrying the information is also lost. Instead, for signals at clock rates up to 1 GHz, varistors with parasitic capacitances up to a max. ca. 1 pF are desirable.
The problem of the present invention is to specify an electrical multi-layer component with low parasitic capacitance.
This problem is solved with a multi-layer component with the features of claim 1. Advantageous constructions of the invention are to be taken from the additional claims.
The multi-layer component is constructed from a stack of ceramic layers, which form a solid body. On the bottom side of the body there are first and second connection surfaces for contacting the component. Between the ceramic layers of the body there are metallization layers in which structured electrode surfaces can be arranged.
All of the electrode surfaces of an electrode structure are electrically connected to each other or to one of the connection surfaces by means of via contacts through the ceramic layers. All of the electrode surfaces connected to each other together form a first electrode structure. The corresponding electrode surfaces connected to one of the second connection surfaces and via contacts form a second electrode structure. The first and second electrode structures are separated and electrically insulated from each other. At least one of the two electrode structures has a via contact with one blind end that does not end in an electrode surface. This end points in the direction of the other electrode structure and forms in this region the shortest distance between the first and second electrode structure. The shortest distance is here measured vertical to the layer planes of the ceramic layers toward the closest metallization layer, in which an element of the other electrode structure is located.
A via contact is understood to be a cylindrical hole, e.g., filled with electrically conductive material, through at least one ceramic layer, which connects a metallization layer to another metallization layer or to a connection surface in a straight line vertical to the layer planes of the ceramic layers. A blind end of a via contact ends in a metallization plane, in which it has absolutely no contact with an electrode surface or a connection surface. The other end of the via contact, however, is always connected to an electrode surface or to a connection surface.
With the exception of the shortest distance in the region of the blind end of the via contact, first and second electrode structures of the multi-layer component run at a large distance, which includes several ceramic layers, from each other. The blind end can also form only a small capacitance to the closest metallic structure of the other electrode structure due to its small surface area. In this way, the parasitic capacitance between the first and second electrode structure is kept low.
In addition, it is advantageous to structure the first and second electrode structures and, in particular, the electrode surfaces belonging to these electrode structures, such that there is no overlap between the electrode surfaces of different electrode structures in the region of the blind via contact. Also, the distance of the electrode surfaces to each other increases and the parasitic capacitance between both electrode structures is further reduced.
The multi-layer component can also be implemented as an HTCC (High Temperature Cofired Ceramic). This material guarantees exact structurability with respect to the position of via contacts and electrode surfaces, so that a multi-layer component with an exactly defined structure and an exactly defined parasitic capacitance can be obtained.
The first and second electrode structure can each have a via contact with one blind end. The two blind ends can then be arranged one above the other in the stack of the body and point towards each other. If the thickness of a single ceramic layer is the shortest distance in the region of these two blind ends, and if the blind via contacts are each connected to an electrode surface, then the minimum distance of said two electrode surfaces corresponds to the layer thickness of the three ceramic layers lying in-between. Preferably, the via contacts are extended by the blind ends, and thus lead in a straight line through several ceramic layers. In this way, the associated electrode surfaces are distanced even farther from each other by the first and second electrode structures.
However, it is not necessary for both electrode structures to have electrode surfaces. It is also possible, for example, that one of the two electrode structures is made from only one via contact, which reaches through possibly several ceramic layers and which is connected to one of the connection surfaces.
In a multi-layer component, several first connection surfaces and a corresponding number of first electrode structures connected to these surfaces can be provided. The several first electrode structures can be separated from each other galvanically and can each have a via contact with one blind end. An overlap with the second electrode structure can then take place exclusively in the region of this blind end, wherein the second electrode structure can also have a via contact with a blind end, for example, in the region of overlap. Several of these first electrode structures can then overlap a single second electrode structure. It is also possible, however, to provide in the multi-layer component both several first electrode structures and also several second electrode structures, where the number of first and second electrode structures need not be equal.
For further minimization of the parasitic capacitance of the multi-layer component, the connection surfaces are distributed on the bottom side of the body so that they are at a maximum distance from each other. This can be achieved in that the connection surfaces are provided at the edges, in the corners, and/or in the middle of the lowermost ceramic layer. Two connection surfaces, which are arranged on the bottom side at two diagonally opposite corners, have the greatest distance from each other. An easily accessible connection surface on the bottom side has a strip-like construction along one edge of the base surface or the body. These connection surfaces can be connected, for example, in the middle by means of via contacts to one or more electrode surfaces.
The electrode surfaces of different electrode structures are preferably arranged in metallization layers far removed from each other. It is also possible to provide only one electrode surface for each electrode structure. Here it is useful for the electrode surfaces to have a strip-like construction and to let them run towards each other starting, e.g., from different corners of the body. For a symmetrical arrangement, an overlap in the middle (relative to the base surface) of the body can be maintained. The one or more via contacts with a blind end are then constructed there, which point from an electrode structure to the corresponding electrode surface of the other electrode structure. Advantageously, the second electrode structure is also provided with a via contact with a blind end. For reasons of symmetry, it is advantageous to construct the blind ends of the via contacts for both electrode structures at the same distance to the associated, closest electrode surface.
If there are several first connection surfaces, then it is advantageous to arrange the second connection surface in the middle. In contrast, it is advantageous to arrange the first connection surface in the corners on the bottom side. Here, the electrode surfaces can also have a strip-like construction and can run from the via contacts arranged above the first connection surfaces in the direction of the body middle, where they overlap corresponding via contacts belonging to the second electrode structure.
If first and second electrode structures are present each in an even number, then an overlap with two electrode structures of different type between each can be realized. This can then take place in a region of the body removed from the connection surfaces. That is, no connection surfaces are provided in the stack underneath the via contacts with the blind ends.
The multi-layer component can be constructed from a varistor ceramic, for example, on the basis of doped zinc oxide. The multi-layer component then represents a varistor with low but defined capacitance. Such a varistor can be used advantageously as an ESD protection component in data lines, which are operated at high clock rates, for example, up to one gigahertz. The low capacitance of the varistor, which does represent a shunt line, prevents the data signal from being diverted to ground via the parasitic capacitance of the varistor forming a high-pass filter and thus from being lost.
The multi-layer component can also be constructed from a ceramic material with negative or positive temperature coefficients of resistance. In this way, it can be used as a PTC or NTC type thermistor.
In addition to the function layers, the ceramic body can include additional layers, which guarantee, for example, the stability of the body. Such layers are then preferably constructed as dielectric layers, in order to generate no new current paths. Additional dielectric layers are then also arranged outside the current path that appears between the first and second electrode structures when the component responds. Such a response of the component is achieved, in the case of a varistor, when the varistor voltage is exceeded between the first and second electrode structures or, in the case of a PTC, when a certain temperature is exceeded.
Below, the multi-layer component is explained in more detail with reference to embodiments and the associated figures. The figures are used for illustrating the invention and are laid out only schematically and not true to scale. Parts that are identical or that have identical functions are designated with identical reference symbols.